1. Technical Field of the Invention
The present invention relates generally to a vehicle control apparatus designed to control an output of an engine mounted in a vehicle in order to ensure the drivability of the vehicle when the engine is restarted automatically.
2. Background Art
There are known engine control systems for automotive vehicles which are designed to perform the so-called idle stop function (also called an automatic engine start/restart function) to stop the engine automatically when the output of the engine is not required, e.g., the brake pedal has been depressed and restart the engine automatically when the engine output is requested, e.g., the accelerator pedal has been depressed. Japanese Patent First Publication No. 2002-242724 teaches an engine control system for vehicles which switches the degree of output torque of an internal combustion engine between when the engine is started in response to turning on of a key made by a vehicle driver and when the engine is started in an idle stop control mode. Specifically, the engine control system decreases the degree of output torque of the engine when the engine is restarted automatically in the idle stop control mode to be below that when the engine is started manually by the vehicle driver in order to minimize starting shock arising from high-rpm idling of the engine. Additionally, when the temperature of cooling water or coolant for the engine is below a given value or a charged state of a storage battery installed in the vehicle is below a given level, the engine control system also restricts or inhibits the decrease in output torque of the engine when restarted, thereby decreasing the starting shock arising from high-rpm idling of the engine and ensuring the stability in starting the engine.
The engine control system is, as described above, designed to ensure the stability in restarting the engine, but however, does not consider the drivability after the engine is restarted. Specifically, even when the decrease in output torque of the engine is restricted to ensure the stability in restarting the engine in the idle stop control mode in conditions where the engine does not start easily, it may result in a lack in output torque of the engine needed to meet requirements imposed by factors such as surrounding conditions of the vehicle or driver's intentions other than relating to the vehicle itself, which leads to the deterioration of the drivability.